US2861609A - Method for producing non-aging silicon-killed steel - Google Patents

Description

Nov. 25, 1958 w. c. LESLIE METHOD FOR PRQDUCING NON-AGING SILICON-KILLED STEEL Filed Jan. 15, 1954 FIE- 1- m 8 .N -QSEQW 57m l, wa f METHOD FOR PRODUCING NON-AGING SILICON-KILLED STEEL William C. Leslie, Cleveland, Ohio, assignor to United States Steel Corporation, a corporation of New Jersey This invention relates to the reduction of strain-aging tendencies of silicon-killed steel and more particularly to a method of heat treating low-carbon, silicon-killed steel to substantially eliminate subsequent strain aging thereof.

There has been considerable confusion in the literature and among the workers in the field concerning the cause of strain aging of W-carbon, i. e. less than .30% carbon, steels. However, it is now well established that the primary cause thereof is nitrogen in solid solution in ferrite. While carbon also affects strain aging, nitrogen is much more effective because of its greater solubility in ferrite at low temperatures. The only feasible method proposed to date of removing this nitrogen from the solution is by alloying the steel with elements which combine with nitrogen to form stable nitrides. Elements which have been successfully used for this purpose are strong deoxidizers, such as aluminum, titanium, vanadium and zirconium. Silicon is a common and inexpensive deoxidizer used to produce killed steels point elongation, removing them from the testing machine, and aging in boiling water. After aging, the specimens were replaced in the tensile testing machine and pulled to fracture. The extent of the strain aging was determined by subtracting the stress at the point at which the load was released (A) from the yield point after aging (B) dividing by A and expressing as a percentage thus B-A A Percent strain aging: X100 Steel 1 Percent Carbon .20 Manganese .80 Phosphorus .01 1 Sulphur .018 Silicon .18 Aluminum .004 Nitrogen .007

This steel was killed by the addition of ferrosilicon in the furnace with slight aluminum additions in the mold.

Specimens of this steel as shown in Figures 1 and 2 of the drawings were austenitized at 2250 F. and 1600 F. followed by air or furnace cooling to room temperature. The tests showed that the strain aging of this steel was substantially unchanged by this treatment, re-

Unid States Patent() maining above 10%. Similar resultsrwerev obtained with specimens from another heat of steel identified as Steel 2 having the following analysis:

Steel 2 Percent Carbon .25 Manganese .50 Phosphorus .013 Sulphur .027 Silicon .23 Aluminum Y .005 which was killed similarly to Steel 1. Specimens thereof along with further specimens of Steel 1 were tested by heating to 1600 F. followed by cooling to room temperature at a rate of 1315 F. As in the foregoing experiment, the strain-aging characteristics of these specimens were relatively unchanged, remaining above 10%.

Contrary to the conclusion to be drawn from the foregoing that silicon-killed steel is unaffected by the foregoing treatments, I have discovered that silicon-killed steels can be rendered substantially non-aging by holding for extended periods of time, i. e. over one hour at temperatures well below the A1 temperature of the steel at a temperature between 1000 and 1200 F.

As a demonstration of my preferred treatment, specimens of Steel 1 were again heated to 2250 F. or 1600 F. and then cooled to 1100 F. and held there for periods of time with the results shown in Figures 1 and 2. Samples of Steel 2 were similarly treated after heating to 1600 F. by holding at 1l00 F. for the times shown on Figure 2.

As clearly shown by the graphs of Figures 1 and 2 holding for times beyond one hour at 1100 F. substantially reduced the strain-aging characteristics of the specimens and that such characteristics were reduced to 2% or less by holding at such temperature for 24 hours.

This minoror residual amount of strain aging is`considered inconsequential.

Tests were also conducted by holding specimens of Steel 1 at 1300" F. for extended periods but as shown on the drawings such treatment had no effect on the strain-aging characteristics.

While I have shown and described two specific embodiments of my invention, it Will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of my invention, as defined in the appended claims.

I claim: v

l. A method of reducing the strain-.aging characteristics of manganese-containing silicon-killed steel characterized by substantial freedom from the strong deoxidizers aluminum, titanium, vanadium and zirconium, with the balance iron and residual elements in common amounts comprising holding the `steel ata temperature above about l000 F. and below about 1200 F. for at least one hour.

2. A method of reducing the strain-aging characteristics of manganese-containing silicon-killed steel characterized by substantial freedom from the strong deoxidizers aluminum, titanium,A vanadium and zirconium, with the balance iron and residual elements in common amounts comprising austenitizing the steel, then cooling it to a temperature above about l000 F. and below about l200 F. and holding it at such temperature for .at least one hour.

3. A method of substantially eliminating the strainaging tendency of manganese-containing low-carbon, silicon-killed steel characterized by substantial freedom from the strong deoxidizers aluminum, titanium, vanadium and zirconium, with the balance iron and residual elements in common amounts comprising holding the steel at about ll00 F. for at least one hour until the strain-aging tendency is reduced to below 2% 4. AY method of substantially eliminating the strainaging characteristics of manganese-containing low-carbon, silicon-killed steel characterized by substantial freedom from the strong deoxidizers aluminum, titanium, vanadium and zirconium, with the balance iron and residual elements in common amounts comprising austenitizing the steel, cooling it to about 1100 F. .and holding it at said temperature for at least one hour until the strain-aging tendency is reduced topless than 2% 5. A method of substantially eliminating the strainaging characteristics of manganese-containing low-carbon, silicon-killed steel characterized by substantial freedom from the strong deoxidizers aluminum, titanium, vanadium and zirconium, with the balance iron 4and residual elements in common amounts comprising austenitizing the steel, cooling it to about 1100 F. and holding it at said temperature for about 24 hours whereby to reduce the strain-'aging tendency to less than 2% 6. A method of substantially eliminating the strainagingcharacteristics of low-carbon, silicon-killed steel containing .30% maximum carbon, 1.50% maximum manganese, .50% maximum silicon with the balance iron and residual elements in common amounts comprising austenitizing said steel, cooling it to about 1100 F. and holding it at said temperature for about 24 hours, whereby to reduce its strain-aging tendency to less than 2% 7. A method of substantially eliminating the strain aging characteristics of low-carbon, silicon-killed steel containing .30% maximum carbon, 1.50% maximum manganese, .50% maximum silicon with the balance iron and residual elements in common amounts comprising austenitizing said steel, cooling it to between 1000 and 1200 F. and holding it at said temperature until its tendency to strain age has been reduced to less than 2%.

References Cited in the ile of this patent Metals and Alloys, vol. 5, May 1934, pages 11G-1712. Atlas of Isothermal Transformation Diagrams, publ. by U. S. S. Corp., 1951, pages 77, 79.

UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,861,609 November 25, 1958 William C. Leslie It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 34., after steels insert the following:

and it 'also has the property of combining with nitrogen to form a stable compound. Despite this latter fact, silicon-killed low-carbon `steels are generally susceptible to strain aging.

It is accordingly an object of this invention to produce silicon-killed lowcarbon steel which is substantially free from the tendency to strain age.

The foregoing and further objects will be apparent from the following speciication when read in conjunction with the attached drawing wherein Figures 1 and 2 are graphs wherein percent of strain aging is plotted against a time log scale for heat treatments as indicated thereon.

We have discovered that silicon-killed low-carbon steel can be rendered substantially free from strain aging by a pro erly conducted heat treatment as hereinafter described. The steel under consideration can be generally defined as containing .30% maximum carbon, 1.50% maximum manganese, .50% maximum silicon with the balance substantially iron and residual elements or impurities in common amounts. Since carbon is a secondary cause of strain aging, the steels under consideration cannot be rendered completely non-aging under all conditions as high a ing temperatures will cause slight strain a ing. To produce a steel completely Free from strain agin would require the addltion of elements which reduce the solubility of both calgbon and nitrogen in ferrite to a very low level.

Y In my work on strain aging in connection with this invention, the extent of strain aging was determined y tensile tests. Thus the strain aging charactlristicdof samples were determined by straining tensile test specimens through t e yie Signed and sealed this 10th day of March 1959.

[smh] Attest: v

KARL H. AXLINE, l ROBERT C. WATSON, Attestng Ocer. Commissioner of Patents.

Claims (1)

1. A METHOD OF REDUCING THE STRAIN-AGING CHARACTERISTICS OF MANGANESE-CONTAINING SILICON-KILLED STEEL CHARACTERIZED BY SUBSTANTIAL FREEDOM FROM THE STRONG DEOXIDIZERS ALUMINUM, TITANIUM, VANADIUM AND ZIRCONIUM, WITH THE BALANCE IRON AND RESIDUAL ELEMENTS IN COMMON AMOUNTS COMPRISING HOLDING THE STEEL AT A TEMPERATURE ABOVE ABOUT 1000*F. AND BELOW ABOUT 1200*F. FOR AT LEAST ONE HOUR.

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